This proposal is directed towards understanding the biochemistry, action and production of a subclass of the colony stimulating factors (CSFs) that stimulates mononuclear phagocyte proliferation (CSF-1). Preliminary studies on the role of carbohydrate in the structure and function of the CSF-1 molecule will be completed. The relationship between the behavior of the CSF-1 receptor and the changes in target cell morphology in the presence of CSF-1 will be investigated. Evidence will be sought for the occurrence of CSF-1 receptors on the bone marrow cells which give rise to spleen colonies in irradiated recipient mice. Attempts will be made to determine the nature and distribution of CSF-1 binding cells and to produce hybridomas making monoclonal antibody to CSF-1.